A traditional mechanism for controlling the intake valve of an internal combustion engine is shown in FIGS. 10 and 11, it mainly includes a cam 200, a rocker 300, a stopper 400 and a spring 500. One end of the rocker 300 engages the cam 200, the other end presses the stopper 400. One end of the spring 500 presses the support 700 which is fixedly secured with respect to the cylinder wall 600, the other end abuts against the flange 800 mounted on the end of the stopper 400. As the cam 200 begins to rotate in clockwise direction from the position shown in FIG. 10, it pushes the left end of the rocker 300 upwardly, the rocker 300 then pivots and its right end presses the stopper 400 downwardly, thus, the stopper 400 overcomes the resistance of spring 500 and moves downwards, then, the intake valve is opened for admission or exhaust. As the cam rotates to the position shown in FIG. 11, the left end of the rocker 200 lowers and the right end rises, thus, under the action of the spring 500, the stopper 400 also rises so that the intake valve is closed for terminating admission or exhaust. As the cam continues rotating, the above course is repeated.
The above described traditional design requires a very large spring force, otherwise, if the rotation is fast, the spring will be incapable of closing the intake valve timely due to its small spring constant. However, if the spring constant is great, the rocker will correspondingly encounter a greater resistance as the cam pushes the rocker. In order to overcome this greater resistance, the engine will consume more energy.